1. Field of the Invention
The present invention relates to a map display method in a navigation system and a navigation apparatus having a bird""s-eye view display function that provides visual effect as though its map image were seen from above obliquely.
2. Description of Related Art
For example, Japanese patent application laid-open No. 7-220055 discloses a navigation system with a bird""s-eye view display function. It carries out calculations needed for the bird""s-eye view display by processing the map data of each predetermined square block according to display parameters such as a display reference point (for example, the position of the vehicle itself) and a display angle, and draws a bird""s-eye view as shown in FIG. 11 using the calculation result. The bird""s-eye view display can provide an enlarged view of the information near the display reference point (the position of the vehicle itself) together with information about distant areas. Accordingly, it can reduce the frequency of map switching, thereby improving its operability.
In FIG. 11, the reference numeral 101 designates a map image region; 102 designates a background image region; 103 designates a horizon representing the boundary between the two regions; 104 designates a retrieved route displayed in the map image region 101; and 105 designates the position of the vehicle itself displayed on the retrieved route 104. At the periphery of the map image region 101, there are displayed a bearing display mark 106, a display mark 107 of the distance to a destination and predicted arrival time, a map transfer switch 108, a position registration switch 109, an image mode switch 110, a distance display mark 111 indicating the distance to the next corner and the like. Besides, current time 112 is displayed on the background image region 102.
With the foregoing configuration, the conventional navigation system has the following problem with the bird""s-eye view display. Although it sets a pseudo horizon 103 as a boundary between the map image region 101 and the background image region 102 that limits the display range of the map image, since the pseudo horizon is a straight line, it provides a viewer with little realism, presenting a problem of being unable to achieve enough effect of the bird""s-eye view display.
The present invention is implemented to solve the foregoing problem. It is therefore an object of the present invention to provide a map display method in a navigation system and a navigation apparatus capable of enhancing a sense of realism by rounding the horizon.
According to a first aspect of the present invention, there is provided a map display method in a navigation system having a bird""s-eye view display function of displaying a map image in conjunction with a background image, the map display method in a navigation system comprises a step of displaying a horizon that indicates a boundary between the map image and the background image, and is rounded at least in part.
Here, the map display method in a navigation system may further comprise the steps of: preparing a plurality of background data to be pasted with different degrees of roundness of the horizon; selecting one of the background data to be pasted in accordance with a display scaling; and displaying the background data with super imposing the background data upon the map data.
The map display method in a navigation system may further comprise the steps of: preparing a plurality of background data to be pasted with different degrees of roundness of the horizon; selecting one of the background data to be pasted in accordance with a vehicle speed; and displaying the background data with superimposing the background data upon the map data.
The horizon may be rounded within a display inhibition region which is adjacent to the background image, and in which display of a land mark or a destination mark of the map image is inhibited.
According to a second aspect of the present invention, there is provided a navigation apparatus comprising: a bird""s-eye view generating section for generating a bird""s-eye view from map data input in accordance with a display target area; a display section for displaying the bird""s-eye view; and a horizontal background data generating section for generating background data including a rounded horizon as a background image to be superimposed upon a map image corresponding to the map data.
Here, the navigation apparatus may further comprise: a memory for storing a plurality of background data to be pasted with different degrees of roundness of the horizon; a display scaling decision section for deciding a display scaling; and a horizontal roundness decision section for deciding a degree of roundness of the horizon in accordance with the display scaling determined by the display scaling decision section, wherein the horizontal background data generating section may read from the memory the background data to be pasted with the degree of roundness determined by the horizontal roundness decision section.
The navigation apparatus may further comprise: a memory for storing a plurality of background data to be pasted with different degrees of roundness of the horizon; and a horizontal roundness decision section for deciding a degree of roundness of the horizon in response to a speed of a vehicle detected by a vehicle speed sensor, wherein the horizontal background data generating section may read from the memory the background data to be pasted with the degree of roundness determined by the horizontal roundness decision section.
The display target area may be decided in accordance with a display scaling, a display angle, a display position and a bearing of a vehicle.